1. Field of the Invention
The present invention relates to a method of effecting a protection control in a communication network and an RPR apparatus suitable for use in a communication network of an EOS (Ethernet Over SONET) in particular, in which a resilient packet ring (RPR) of the Ethernet (R) is placed upon a bidirectional line-switched ring (BLSR) composed of a plurality of synchronous optical network (SONET) apparatus, i.e., a ring network formed of the BLSR is connected with the RPR apparatus.
2. Description of the Related Art
Recently, the Internet becomes more and more widely deployed in a communication field and with this trend, amount of communication information exchanged by means of IP (Internet Protocol) is remarkably increased. The IP communication is originally developed for data communication as a main object. Therefore, the IP communication has not been requested to have a high real time property as compared with a voice communication. Accordingly, even if any failure is brought about in the communication network, the communication network can be relatively free from a severe demand that might be imposed on the communication network in terms of a period of time it takes for the communication network to restore a network failure.
However, communication service demand has been steadily increased in the IP communication. As a consequence, the application field of the IP communication is expanded. At the same time, it is requested to provide a more reliable communication network. However, owing to the establishment of an RPR technology, high reliability can be secured even in the IP communication.
In this case, RPR is a technology which exerts its optimum performance upon data traffic in a network such as Ethernet. The RPR technology also has a historical background as has been developed as a ring network which is endurable in the requested reliability of WAN (Wide Area Network). In the RPR technology, an Ethernet frame is encapsulated within an RPR frame so that the Ethernet frame can function as a part of the RPR ring network.
On the other hand, the conventional SONET transmission network has been mainly developed as a network for communication with a speech signal and the network comes to have a large size in infrastructure. When the network employing the above-mentioned RPR technology is requested to be constructed by using the technology of the current status with ease effectively, it is considered that to introduce the infrastructure of the SONET transmission network into the network employing the above-mentioned RPR technology is an effective means.
In this case, the BLSR is a SONET network formed as a ring. According to the arrangement of the protection function of the BLSR, the network is provided with a redundant network in which a signal is allowed to be transmitted in a direction of the ring inverse to the direction in which the signal is ordinarily transmitted through a working network. With this arrangement, when any failure is brought about in the work network, the signal path can be switched from the working network to the network provided as a redundancy, and the failure can be recovered.
The RPR technology has been developed with an intention that the IP communication system comes to have a protection function having a reliability substantially equivalent to that of the conventional SONET transmission system. The protection function based on the RPR technology can be realized in the following manner in Ethernet ring network, for example. That is, packets assigned with different priority orders are ordinarily transmitted through the ring network bidirectionally. If any failure is brought about in the network for transmitting the packets in one direction of the ring path, the packet transmission is changed from the network suffering from the failure to one having no failure. At this time, the packets are brought into a transmission process one by one in accordance with the priority orders which are assigned to the packets in advance, respectively. That is, a packet having relatively high priority order is transmitted prior to one having relatively low priority order.
In this case, when the RPR transmitting apparatus (RPR apparatus) is provided in the SONET network, arrangement is made on the network operation in such a manner that the protection function of the SONET is effected prior to the protection function of the RPR apparatus. In more concretely, when any failure is detected in the RPR apparatus and the protection function is activated in the manner described above, a delay time is set in the network by user's manual input (key input operation through a user interface).
However, according to the above-described conventional technology, even if the RPR apparatus is equipped with a protection switching function which is highly reliable and capable of operating at a high speed, it takes a long period of time for switching from the network under current working status to the redundant network upon effecting the SONET protection function for failure restoration. As a consequence, the reliability (a networking rate) of the network can be lowered. Further, if the delay time is set to zero, it is expected that the protection switch of the SONET and the protection switch of the RPR apparatus conflict with each other.
The conflict of the protection switch of the BLSR and the protection switch of the RPR apparatus is taken place in the following manner. That is, for example, the switching of the RPR protection is effected on one network failure and thereafter the switching of the BSLR is effected on the same network failure. Then, the RPR apparatus perceives that the failure is restored, and hence the RPR apparatus tries to return the switching status to one which the protection switch of the RPR took before the failure was brought about. As a consequence, unstable reciprocal switching motion can be brought about in the RPR switch. In this case, either of the switching operation of the RPR apparatus or that of the BLSR is sufficient for restoring the failure.
In other words, the conflict of the protection functions results in useless switching motion, which fact can cause an undesirable hit (signal jump).